Study on the optical properties of Er, Yb: KY(WO4)2 nanoparticles doped with different concentrations of Na+ ions

Highlights: • The effect of structural transformation of nanoparticles Er,Yb: Na_xK_1-xY(WO₄)₂ is studied. • The fluorescence properties were analyzed by Judd–Ofelt theory. • Doped ions can induce the structural transformation of the matrix to increase the fluorescence intensity. The 5%Er,15%Yb: Na_xK_1-xY_0.8(WO₄)₂ (Er, Yb: NKYW) nanoparticles were successfully prepared using a solid-phase method, and the structure and properties of the nanoparticles were characterized via X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Fourier infrared spectroscopy (FT-IR), photoluminescence spectroscopy, and fluorescence decay curve. The analysis of the obtained data showed that the structure of the nanoparticles experienced a monoclinic to tetragonal transformation due to an increase in the doping concentration of Na⁺, which in turn changed the luminescence intensity. The highest luminescence intensity was obtained when the Na⁺ ion doping concentration was 50%, thereby indicating the effect of the structural change on the luminescence intensity. To illustrate the gain mechanism of the structure on the fluorescence intensity, the Judd-Ofelt (J-O) theory and energy transfer efficiency were used. The results indicate that the change in the luminescence of Er, Yb: NKYW nanoparticles is due to the combination of two independent mechanisms, namely: Yb³⁺ induced sensitization and Na ⁺ induced structural transformation. Therefore, this study provides potential values for application of nanoparticles in the fields of optical display, biofluorescent labeling, and optical anti-counterfeiting.